In recent years, there has been a trend towards integrating many of the traditional single purpose weight lifting exercise machines used to increase muscular strength into a fewer number of multipurpose machines. These integrated weight machines were designed to provide numerous articulating resistive exercises in less space than would otherwise be required when using dedicated machines.
The initial embodiment of these multipurpose machines involved the use of dedicated weight stacks for each station, with the stations being located about a single structure. Thus, while the overall footprint of the machine was less than that of the sum of the footprints of single purpose weight lifting machines, the total amount of materials used, especially the weights used, remained nearly the same.
Later improvements to the concept of a multipurpose weight machine utilized fewer weight stacks or a centralized weight stack that was connectable to a plurality of exercise stations. While this method of constructing the machine decreased the total amount of weights necessary, it required a user to "set up" the machine for each desired exercise, e.g., connecting the desired station's cable to the weight stack after disconnecting the cable from another station.
An inherent shortcoming regarding cable lift systems, however, is the inevitable stretching of the cables, especially when lifting great weight. Cables of the type commonly used in weight lifting machines yield slightly during initial loading that occurs when lifting a weight stack or generally overcoming a resistive force. This slight yielding or stretching results in a "spongy" feel) perceived by the user. It is therefore desirable to construct a multipurpose weight machine that reduces or eliminates the stretch potential of cables subject to large lifting forces.
Another shortcoming regarding multipurpose weight lifting machines concerns the bench press station. When engaging in the bench press lifting exercise using free weights, the path of extension and flexion is determined by the user. This permits the user to lift weights in the most natural and efficacious manner. However, when operating a bench press station in a weight lifting machine, traditional methods have provided for a press arm wherein either the distal portion was pivotally connected to the machine's frame and the proximal portion comprised the press bar wherein the arm would swing in an arcuate path, or a linear lift press arm wherein the distal portion was translatable along a vertical track thereby confining the arm to a linear path. In both methods, the weights were connected to the arm at a point generally intermediate the distal and proximal portions.
Two consequences resulted from the geometry used in the pivoting arm method, depending upon the means employed to lift the weight stack. First, because the weight is attached at a midpoint a mechanical advantage results in a decreased effective weight at the lift point. Consequently, a load must be presented to the lifting bar that is greater than would be necessary if there was no mechanical advantage. Second, either a flexible link was needed to attach the weight stack to the arm of the press (a link pivoting at both the weight stack to link connection and the link to arm connection) or a follower that traveled along the arm was needed to translate the arcuate motion of the arm to linear motion of the weight stack.
When using the follower connection, the arcuate motion of the arm was effectively translated into linear motion of the weight stack, however, the user encountered progressively greater resistance to lift effort as the follower moved the arm to weight stack connection location progressively towards the press bar during extension of the arms, thus losing mechanical advantage. When using a pivoting link, the effective weight lifted by a user would not appreciable change, however, the weight stack would tend to bind against the guide rods of the stack because the vector of the lifting force would no longer be parallel to the guide rods. As with the follower solution, the nature of the press bar lifting path was not changed. Finally, if a rigid link was used between the press bar and the weight stack, then the weight stack must be pivotal at the base to accommodate the arcuate path of the press bar and arm.